User Manual

3.10 FFT Analysis Modes
101
Waveform Example
Power Spectrum Density (Linear Predictive Coding) LPC
When the spectrum shape is complex and hard to comprehend with either linear or power spectra, a
rough spectrum structure can be obtained.
Not available with external sampling enabled.
Main uses:
To obtain a spectral envelope using statistical methods
See About the Functions "3.10.2 Analysis Mode Functions" (⇒ p. 102)
Axis Display Type Description
X axis
Linear
Frequency is displayed with equal spacing
Display Range: DC to the top of the frequency range
Log
Frequency is displayed logarithmically
Display Range: 1/400
th
to 1/4000
th
(depending on the number of analysis
points) to the top of the frequency range
Y axis
Lin-Mag Analysis values are displayed linearly.
Log-Mag (logarithm) Analysis values are displayed as dB values. (0 dB reference value: 1eu
2
/Hz)*
* eu: engineering units that are currently set are the standard (e.g., when the unit settings is volts, 0 dB = 1 V
2
/Hz)
X axis: Log
Y axis: Lin-Mag
X axis: Log
Y axis: Log-Mag
• Always specify the order (from 2 to 64). Higher orders can expose finer spec-
tral details.
• Amplitude values provided by LPC are not always the same as the power
spectrum density.
• If an error occurs during analysis, no waveform is displayed.
• Noise-like phenomena can strongly affect the spectrum shape.